Non-Cyanide Electrodeposited Ag–PTFE Composite Coating Using Direct or Pulsed Current Deposition

The effects of FC-4 cationic surfactant on electrodeposited Ag–PTFE composite coating using direct or pulsed currents were studied using scanning electron microscope (SEM), energy dispersive X-ray (EDS), optical microscope, and a linear tribometer. FC-4:PTFE in various ratios were added to a non-cyanide succinimide silver complex bath. Direct or pulsed current method was used at a constant current density to enable comparison between both methods. A high incorporation rate of PTFE was successfully achieved, with pulsed current being highly useful in increasing the amount of PTFE in the composite coating. The study of coating wear under sliding showed that a large majority of the electrodeposited coatings still managed to adhere to the substrate, even after 10 wear cycles of sliding tests. Performance improvements were achieved on all the samples with a coefficient of friction (CoF) between 0.06 and 0.12

Electrochemical micromachining: An Introduction

Copyright © 2016 The Author(s). Electrochemical machining (ECM) is a relatively new technique, only being introduced as a commercial technique within the last 70 years (1). A lot of research was conducted in the 1960s and 1970s but research on electrical discharge machining (EDM) around the same time slowed ECM research (2). The main influence for the development of ECM came from the aerospace industry where very hard alloys were required to be machined without leaving a defective layer in order to produce a component which would behave reliably (3). ECM was primarily used for the production of gas turbine blades (2) or to machine materials into complex shapes that would be difficult to machine using conventional machining methods (4). Tool wear is high and the metal removal rate is slow when machining hard materials with conventional machining methods such as milling. This increases the cost of the machining process overall and this method creates a defective layer on the machined surface (3). Whereas with ECM there is virtually no tool wear even when machining hard materials and it does not leave a defective layer on the machined surface. This paper reviews the application of electrochemical machining with regards to micro-manufacturing and present state of the art micro ECM considering different machined materials, electrolytes and conditions used.The research reported in this article was supported by the European Commission within the project ‘Minimizing Defects in Micro-Manufacturing Applications (MIDEMMA)’ (FP7-2011-NMP-ICT-FoF-285614)

The electrodeposition and characterisation of compositionally modulated tin-cobalt alloy coatings as lead-free plain bearing material

Traditionally, lead-based bearing overlays dominate the commercial automotive market and it has been proven that an excellent combination of properties can be attained through their use. However, lead is a toxic metal and a cumulative poison in humans. According to the European Union End-of-Life Vehicle (ELV) Directive proposed in 1997, vehicles that registered in'all the member states after 1st July 2003 should contain no lead, mercury, cadmium and hexavalent chromium. In this study, a new sulphate-gluconate electrolyte was used to produce multilayer SnCo coatings, aimed at a lead-free overlay for future market use. Tin-cobalt compositionally modulated alloy (CMA) coatings produced from sulphategluconate electrolytes have been previously examined as a potential replacement for lead-free bearing overlays [1]. However, some obstacles may exist which limit their potential use on an industrial scale. For example, long electroplating times are required to produce a thick coating which is very undesirable from an industrial viewpoint, and also the possible elemental interdiffusion occurring in the coating system under engine operating temperatures could rapidly deteriorate the coating properties. In addition, there is an increasing demand from automotive industry to further improve bearing overlay properties, for example for high performance and high compression ratio engines... cont'd

Zinc based composite coatings as an alternative to electrodeposited cadmium

Cadmium coatings are currently applied to steel fasteners used in aerospace applications. At present there are growing concerns, based on cadmium's toxicity and carcinogenicity, which may lead to its eventual banning. The aim of this research, therefore, was to find a possible replacement to electrodeposited cadmium for use on aerospace fasteners. Any replacement coating system should have all of the relevant properties that make cadmium so attractive, but without its obvious shortcomings. These beneficial properties include excellent corrosion resistance in chloride containing media (such as seawater), the ability to offer sacrificial protection to steel, excellent galvanic compatibility with most aluminium alloys and an inherent lubricity. Alternatives proposed and produced in this research are electrodeposited composite coatings containing PTFE particles, based on zinc or zinc alloys. Extensive analysis was carried out in order to characterise the coatings. Composition was determined by a number of methods; gravimetric analysis was used to determine the percentage of codeposited PTFE, while X-ray and X-ray wavelength energy dispersive analysis were used to determine the percentage of alloy element present in these coatings. Coating morphology was investigated by scanning electron microscopy. The sacrificial corrosion performance of each coating in relation to steel was studied using neutral salt-spray tests, while linear polarisation resistance tests gave an indication of their barrier corrosion properties. Galvanic compatibility of the coatings with aerospace grade aluminium alloys was investigated using a zero resistance ammeter. Two different tribological tests, an inclined plane test and a reciprocating wear test, were used to determine the coefficient of friction for the coatings. Finally, linear sweep voltammetry was used to compare the kinetics of electrodeposition from dilute solutions and corrosion in aqueous media for each of the coating systems. The composite coatings were found to offer either similar or slightly reduced corrosion performance to conventional zinc and zinc alloy coatings, but were inferior to commercially electrodeposited cadmium. However, the tribological properties of these coatings demonstrated a marked improvement over cadmium

The influence of particle type and process conditions on electrodeposited composite coatings

Composite materials are usually multi-phase materials, made up from two or more phases, which are combined to provide properties that the individual constituents cannot. This technology represents an economical way to improve product performances avoiding the use of expensive materials. Composite materials can be obtained as films by means of the electrolysis of electroplating solutions in which micrometre- or submicrometre-size particles are suspended: variable amounts of these particles become incorporated in the electrochemically produced solid phase, to which they impart enhanced properties. The main aims of the present work contributing to this thesis are the study of different parameters influencing the electroco-deposition process in order to promote and improve the applicability of such a technology in the high speed electroplating industry. Following a comprehensive review on the electroco-deposition of composite coatings, the phenomena have been analysed moving from a microscopic point of view i. e. the role of the metal ions present in the electrolyte and adsorption on the inert particles and their interactions with the growing metal layer, to a macroscopic point of view i. e. the electrolyte agitation, its influence on particle motion and all the issues related to the presence of particles in an electrolyte during electroplating. In particular the inert particle influence in terms of geometry, dimension and chemical nature (spherical polystyrene particles vs. irregular alumina particles with different dimensions), the metal matrix influence (nickel, copper and zinc), the influence of electrolyte agitation (using a Rotating Cylinder Electrode cell system) and the influence of the coating thickness on particle content in the final coating, using different deposition times, have been examined. The importance of the particle shape has been highlighted showing how incorporating irregular geometries gave higher particle incorporation densities than regular geometries. The influence of the substrate finishing in terms of imperfections has been related to the particle incorporation rate showing how small surface imperfections enhanced the incorporation of particles. Different hydrodynamic regimes have been analysed resulting three different regimes being discerned: laminar, transitional and turbulent. The consequence, in terms of particle incorporation levels, has been found showing how the amount of particles in the coating changed from one regime to another. Different rate-determining steps were related to the hydrodynamics: when the regime is laminar, particles were incorporated as agglomerates and the process was under particle transfer control, whilst in the turbulent zone, the rate determining step was the velocity of reduction of the ions adsorbed on the particle surface

The electrodeposition of compositionally modulated multilayer coatings for enhanced corrosion resistance

The concept of electrodeposited multilayer coatings has been examined using both a dual and single bath process route. The effectiveness of an electrodeposition coating technique was initially investigated on the copper–nickel system. Compositionally modulated metallic coatings (CMMCs) were formed by the alternate electrodeposition of copper and nickel. Individual layer thicknesses were varied from 10 nm to 2 μm by close control of the plating current density with a computer assisted pulse plating facility. Following successful deposition of CMMCs using the copper–nickel system, investigations were concentrated on the zinc–nickel system on steel substrates again both dual and single bath techniques were utilised , the former to produce CMMCs of alternate zinc and nickel as well as layered structures of either zinc or nickel with a commercial zinc–nickel alloy. A single bath technique was used to produce compositionally modulated alloy multilayer coatings (CMAMCs) consisting of alternate layers of two compositions of zinc–nickel alloy. Conventional salt spray and more rapid electrochemical corrosion tests were carried out to assess the effectiveness of the layered coatings, as well as scanning electron microscopy and dispersive X-ray analysis to study the morphological and compositional changes in the coating structures. Results indicate the improvements of corrosion resistance of many of layered structures over similar (in thickness) conventional electrodeposited zinc coatings

Monolithic integration of high-aspect-ratio microstructures with CMOS circuitry

This work involves developing processing techniques for monolithically integrating a high-aspect-ratio microstructures with CMOS circuitry. A microsystem comprising of a microprobe array and signal processing circuitry is utilized as a test vehicle to demonstrate this fabrication process. One potential application of this microsystem is for recording neural signals from the central nervous system. The main results include thick photoresist processing, DC and pulse electroplating to form high-aspect-ratio microprobes, microprobe sharpening and developing a post-IC monolithic integration process. SU-8 is utilized for thick photoresist application. This work focuses on realization of a deep microrecess array in thick resists rather than traditional stand-alone SU-8 columns. The former encounters more processing challenges. Several novel techniques are developed including a unique development step, which results in clean microrecesses up to 450 &181;m deep with the smallest width of 40 &181;m giving aspect-ratio of 11. Electroplating is performed in nickel sulfamate electrolyte. DC plating rate is found to depend on probe location, dimension and probe spacing. Nernst diffusion boundary layer model is utilized to estimate Ni ion diffusion coefficient to be 3.3&215;10&178;-6 cm&178;2 /s. Stress in deposit is found to change from compressive to tensile with increasing DC plating current density and with increasing deposit thickness saturating respectively at 92 MPa and 73 MPa. Stress in pulse plated Ni with long pulses saturates at 54.5 MPa, while short pulse periods produce only compressive stresses between -110 MPa and -160 MPa. Surface morphology of electroplated Ni is related to built-in stress. A one-dimensional simplified model is built to describe the pulse plating process taking fixed and moving boundary approaches. The results are utilized to determine the pulse on time for plating into deep microrecesses. Nickel wire or probe is sharpened electrochemically with wires giving sharper tips under conditions of 30 &176;C, 4 V potential in a 0.5 M sulfuric acid electrolyte. Chemicals are carefully tailored in developing post-IC monolithic integration process to avoid detrimental impact on the CMOS circuitry with processing temperature maintained below 100 &176;C to avoid circuit degradation. A unique chip-level tape-and-wire bonding technique is developed to perform chip-level monolithic integration

Frontiers in Ultra-Precision Machining

Ultra-precision machining is a multi-disciplinary research area that is an important branch of manufacturing technology. It targets achieving ultra-precision form or surface roughness accuracy, forming the backbone and support of today’s innovative technology industries in aerospace, semiconductors, optics, telecommunications, energy, etc. The increasing demand for components with ultra-precision accuracy has stimulated the development of ultra-precision machining technology in recent decades. Accordingly, this Special Issue includes reviews and regular research papers on the frontiers of ultra-precision machining and will serve as a platform for the communication of the latest development and innovations of ultra-precision machining technologies

Developments in non-conventional machining for sustainable production - a state of art review

Abstract